The term “ventilator” is used herein to refer collectively to respirators and ventilators, including various high frequency ventilators. In a hospital, patients may need the assistance of a ventilator when they cannot breathe on their own. Ventilators are expensive machines, and consequently hospitals tend not to have a large number of excess ventilators. Pandemics are relatively infrequent, but potentially devastating mass casualty events. There have been three influenza pandemics in the past century, and an estimated 32 in the past 400 years. In the event of a pandemic, such as that which might be caused by a mutant form of Influenza H5N1, which is already endemic in wild birds and domestic fowl throughout Asia, the number of patients that need ventilators may exceed the available supply. Estimates of the magnitude of the shortage indicate that from 30% to 200% more ventilators will be needed in a pandemic situation. During such a shortage, physicians may be faced with the unpleasant decision of terminating the use of a ventilator by one patient so that another patient may use it, or of withholding ventilator support from a new patient in need. In some situations, terminating or failing to provide the use of a ventilator, even temporarily, will result in a prolonged recovery time for a patient, harm to the patient, or even loss of the patient's life.
A single ventilator can be used to support several patients simultaneously, thereby increasing the number of patients who can be treated, but existing technology does not prevent cross contamination. That is to say that when patients share a ventilator using existing technology, the diseases, bacteria and viruses, carried by one patient may contaminate the environment and equipment used by another patient, and may be directly transmitted to the other patient. Furthermore, existing technology for sharing a ventilator severely limits the capacity to accommodate each individual patient's separate respiratory support needs because no mechanism is provided to separately accommodate each patient's respiratory needs, such as, for example, individualized tidal volume, peak pressure, oxygen concentration, and positive end-expiratory pressure (“PEEP”).
There has been no prior description of the use of a re-breathing circuit to allow aseptic sharing of a ventilator among two or more patients. U.S. Pat. No. 6,675,799 (the “'799 patent”) describes a re-breathing device that was intended to isolate a single patient from his/her ventilator, caregivers, and environment. However, the '799 patent does not disclose how to ventilate more than one patient at the same time using a single ventilator. Nor does the '799 patent address: (1) how to reduce patient tidal volume below the volume delivered to the device by a shared ventilator; (2) how to limit peak airway pressure below that set on the shared ventilator, (3) how to individualize oxygen concentration of patients sharing a ventilator; (4) how to increase PEEP above that set by a shared ventilator; or (5) how to conserve oxygen when several patients share a ventilator, all of which may be essential to the individualization of patient settings during shared ventilation. By way of contrast, an isolation device according to the present invention has the ability to alter the delivery conditions of breathing-gas and thereby individualize the characteristics of the breathing-gas patients receive using a ventilator that may be shared among several patients. This capability to alter the conditions under which breathing-gas may be provided to a patient using a disposable device, allows an inexpensive ventilator, having little sophistication, to deliver breathing-gas having better defined pressure, volume, and oxygen concentration characteristics to a patient.
Additionally, ventilators operate by using a supply of compressed gas to mechanically ventilate the lungs of a patient by increasing the pressure in the patient's airway. Typically, a ventilator requires both compressed air and compressed oxygen, in varying ratios depending on a patient's needs. Less-expensive ventilators, like those stockpiled for pandemic preparedness, may not make efficient use of the gases supplied. This inefficiency is inconsequential with regard to compressed air because, in hospitals, mechanical compressors can be used to generate a continuous supply of pressurized air on-site, so shortages of compressed air are not anticipated, even during a pandemic. Compressed oxygen, however, is usually generated by gas suppliers located off-site and is generally provided to hospitals as compressed oxygen in tanks, or as liquid oxygen. In a pandemic, shortages of both compressed and liquid oxygen are anticipated. Oxygen concentrators can be used to generate oxygen for spontaneously breathing patients, but cannot be used with most ventilators since most ventilators require a pressurized gas inflow at a pressure higher than can be generated by a typical oxygen concentrator. It would therefore be advantageous to have a system, which reduces the amount of oxygen required for mechanical ventilation by using only compressed air to power lung inflation and an efficient re-breathing device to provide oxygen to the patient. No means has previously been described to conserve available oxygen when using less-expensive ventilators to cope with the expected shortage of pressurized oxygen or during a shortage of more advanced ventilators. The use of a re-breathing device to conserve oxygen would help meet these needs.
During a mass casualty event, deploying disposable isolation devices to conserve oxygen and convert inexpensive, unsophisticated, oxygen-wasteful ventilators into affordable, yet more sophisticated, oxygen conserving, isolating ventilators, could save lives. This is not foreseen by the '799 patent.